Why Starlin Castro over Rob Refsnyder? Why Ben Zobrist over Starlin Castro?

March 25, 2016 is about a week before opening day.  It's also the day after Starlin Castro turns 26 years old and it's the day before Rob Refsnyder turns 25.

Starlin Castro is a proven major league shortstop.  Rob Refsnyder is a minor league second baseman of unknown (at least to the public) fielding ability.  In the regular season Castro has played 7,424 innings at shortstop and 258 at second base; Castro was switched to second for the final 38 games of 2015.  In the minors Refsnyder has played 2,948 innings at second base and 428 (358 in his first season of 2012) in the outfield.  So overall Refsnyder has much more experience playing second base.

Castro is a proven major league hitter: 3,763 PA, .725 OPS.  Refsnyder is a proven AAA minor league hitter: 858 PA, .794 OPS. Both bat right handed.

Castro: December 8, 2015: Traded by the Chicago Cubs to the New York Yankees for Adam Warren and player to be named.

The player to be named later is veteran shortstop Brendan Ryan who can also play second and third.  Ryan has played 629 innings at second.  Ryan's salary for 2016 is one million dollars.

Pitcher Adam Warren will be eligible for salary arbitration for the first time, so his pay should increase considerably over the $572,600 he received in 2015.  Maybe he'll get $2 million.  If so, the Yankees might shed $3 million minus the minimum for two players, let's say at $550,000 each.  So the Yankees would save less than $2 million.

Refsnyder had 47 PA with the Yankees in 2015; .859 OPS.  Refsnyder will still be a rookie in 2016 if he plays in the majors.  His salary for 2016, 2017, 2018 will be about the minimum, let's say it averages $600,000 per season for a total of $1.8 million, depending on the new collective bargaining agreement.  In 2019 Refsnyder would be eligible for salary arbitration and possibly a substantial increase.

Here is what the Yankees owe Starlin Castro:

2016	26	New York Yankees	$7,857,143	5.150
2017	27	New York Yankees	$9,857,143
2018	28	New York Yankees	$10,857,143
2019	29	New York Yankees	$11,857,143
2020	30	New York Yankees	*$16,000,000		$16M Team Option, $1M Buyout
		Earliest Free Agent: 2020

What does it say about Rob Refsnyder that the Yankees would pay so much more for Starlin Castro?  What does it say about Starlin Castro that the Chicago Cubs would pay Ben Zobrist, his replacement:

2016	35	Chicago Cubs	$10,500,000	8.134
2017	36	Chicago Cubs	$16,500,000
2018	37	Chicago Cubs	$16,500,000
2019	38	Chicago Cubs	$12,500,000
		Earliest Free Agent: 2020

Note the age difference.  Zobrist is nine years older than Castro.  In 5,013 PA, Zobrist has .786 OPS.  OPS+:
Zobrist 117
Castro 97

So Zobrist is a better hitter and bats lefty.  And Zobrist can play multiple positions well, although only one at a time.  But Zobrist was signed as a free agent by the Cubs specifically to replace Castro at second base.  Zobrist has played a total of 9,902 innings in the majors, 4,825 at second, 3,176 in the outfield.  The Cubs prefer Zobrist even though he has played only 48.7% of his major league innings at second base.

Teams know their own players better than anyone.